(1) Field of the Invention
The present invention relates to the exercise of control over the periodic delivery of current to a load and particularly an inductive load. More specifically, this invention is directed to apparatus for controlling the opening and closing of solid-state switch devices through which current is delivered to a load and especially to a drive system for vibratory feeders which include an electromechanical actuator. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
(2) Description of the Prior Art
While not limited thereto in its utility, the present invention is particularly well suited for use as a drive system for an electromagnetic vibrator and specifically a feed control drive which has the capability of adjusting the amplitude and frequency of the driven mechanism. Drive systems for electromagnetic vibrators are well known in the art. The prior art drive systems include the non-power resonant type, as exemplified by U.S. Pat. No. 3,922,589, and the power resonant type; the present invention being concerned with power resonant drive systems.
Prior art vibrator feed drives, whether power resonant or non-resonant, suffered from common deficiencies. The foremost deficiency resulted from the use of transistors as the main current switching devices. As is well known, transistors are susceptible to destruction as a result of line transients and are limited in the output power which can be obtained. Additionally, prior art attempts to provide a start-up delay, wherein feed drive would be precluded until system voltages had stabilized, had been characterized by complexity and lack of reliability.